Dorota B. Pawlak

Childhood obesity: public-health crisis, common sense cure

During the past two decades, the prevalence of obesity in children has risen greatly worldwide. Obesity in childhood causes a wide range of serious complications, and increases the risk of premature illness and death later in life, raising public-health concerns. Results of research have provided new insights into the physiological basis of bodyweight regulation. However, treatment for childhood obesity remains largely ineffective. In view of its rapid development in genetically stable populations, the childhood obesity epidemic can be primarily attributed to adverse environmental factors for which straightforward, if politically difficult, solutions exist.

Effects of dietary glycaemic index on adiposity, glucose homoeostasis, and plasma lipids in animals

BACKGROUND Clinical studies suggest a role for dietary glycaemic index (GI) in bodyweight regulation and diabetes risk. However, partly because manipulation of GI can produce changes in potentially confounding dietary factors such as fibre content, palatability, and energy density, its relevance to human health remains controversial. This study examined the independent effects of GI in animals. METHODS Partially pancreatectomised male Sprague-Dawley rats were given diets with identical nutrients, except for the type of starch: high-GI (n=11) or low-GI (n=10). The animals were fed in a controlled way to maintain the same mean bodyweight in the two groups for 18 weeks. Further experiments examined the effects of GI in rats in a cross-over design and C57BL/6J mice in a parallel design. FINDINGS Despite having similar mean bodyweight (547.9 [SE 13.4] vs 549.2 [15.2] g), rats given high-GI food had more body fat (97.8 [13.6] vs 57.3 [7.2] g; p=0.0152) and less lean body mass (450.1 [9.6] vs 491.9 [11.7] g; p=0.0120) than those given low-GI food. The high-GI group also had greater increases over time in the areas under the curve for blood glucose and plasma insulin after oral glucose, lower plasma adiponectin concentrations, higher plasma triglyceride concentrations, and severe disruption of islet-cell architecture. Mice on the high-GI diet had almost twice the body fat of those on the low-GI diet after 9 weeks. INTERPRETATION These findings provide a mechanistic basis for interpretation of studies of GI in human beings. RELEVANCE TO PRACTICE The term GI describes how a food, meal, or diet affects blood sugar during the postprandial period. GI as an independent factor can cause obesity and increase risks of diabetes and heart disease in animals. Use of low-GI diets in prevention and treatment of human disease merits thorough examination.

Should obese patients be counselled to follow a low-glycaemic index diet? Yes.

A reduction in dietary fat has been widely advocated for the prevention and treatment of obesity and related complications. However, the efficacy of low‐fat diets has been questioned in recent years. One potential adverse effect of reduced dietary fat is a compensatory increase in the consumption of high glycaemic index (GI) carbohydrate, principally refined starchy foods and concentrated sugar. Such foods can be rapidly digested or transformed into glucose, causing a large increase in post‐prandial blood glucose and insulin. Short‐term feeding studies have generally found an inverse association between GI and satiety. Medium‐term clinical trials have found less weight loss on high GI or high glycaemic load diets compared to low GI or low glycaemic load diets. Epidemiological analyses link GI to multiple cardiovascular disease risk factors and to the development of cardiovascular disease and type 2 diabetes. Physiologically orientated studies in humans and animal models provide support for a role of GI in disease prevention and treatment. This review examines the mechanisms underlying the potential benefits of a low GI diet, and whether such diets should be recommended in the clinical setting.

Glycation-altered proteolysis as a pathobiologic mechanism that links dietary glycemic index, aging, and age-related disease (in nondiabetics)

Epidemiologic studies indicate that the risks for major age‐related debilities including coronary heart disease, diabetes, and age‐related macular degeneration (AMD) are diminished in people who consume lower glycemic index (GI) diets, but lack of a unifying physiobiochemical mechanism that explains the salutary effect is a barrier to implementing dietary practices that capture the benefits of consuming lower GI diets. We established a simple murine model of age‐related retinal lesions that precede AMD (hereafter called AMD‐like lesions). We found that consuming a higher GI diet promotes these AMD‐like lesions. However, mice that consumed the lower vs. higher GI diet had significantly reduced frequency (P < 0.02) and severity (P < 0.05) of hallmark age‐related retinal lesions such as basal deposits. Consuming higher GI diets was associated with > 3 fold higher accumulation of advanced glycation end products (AGEs) in retina, lens, liver, and brain in the age‐matched mice, suggesting that higher GI diets induce systemic glycative stress that is etiologic for lesions. Data from live cell and cell‐free systems show that the ubiquitin–proteasome system (UPS) and lysosome/autophagy pathway [lysosomal proteolytic system (LPS)] are involved in the degradation of AGEs. Glycatively modified substrates were degraded significantly slower than unmodified substrates by the UPS. Compounding the detriments of glycative stress, AGE modification of ubiquitin and ubiquitin‐conjugating enzymes impaired UPS activities. Furthermore, ubiquitin conjugates and AGEs accumulate and are found in lysosomes when cells are glycatively stressed or the UPS or LPS/autophagy are inhibited, indicating that the UPS and LPS interact with one another to degrade AGEs. Together, these data explain why AGEs accumulate as glycative stress increases.

Effects of a low–glycemic load diet in overweight and obese pregnant women: a pilot randomized controlled trial

BACKGROUND The optimal diet for pregnancy that is complicated by excessive weight is unknown. OBJECTIVE We aimed to examine the effects of a low-glycemic load (low-GL) diet in overweight and obese pregnant women. DESIGN We randomly assigned 46 overweight or obese pregnant women to receive a low-GL or a low-fat diet. Participants received carbohydrate-rich foods, fats, and snack foods through home delivery or study visits. The primary outcome was birth weight z score. Other endpoints included infant anthropometric measurements, gestational duration, maternal weight gain, and maternal metabolic parameters. RESULTS There were no significant differences in birth weight z score or other measures of infant adiposity between groups. However, in the low-GL compared with the low-fat group, gestational duration was longer (mean ± SD: 39.3 ± 1.1 compared with 37.9 ± 3.1 wk; P = 0.05) and fewer deliveries occurred at ≤ 38.0 wk (13% compared with 48%, P = 0.02; with exclusion of planned cesarean deliveries: 5% compared with 53%; P = 0.002). Adjusted head circumference was greater in the low-GL group (35.0 ± 0.8 compared with 34.2 ± 1.3 cm, P = 0.01). Women in the low-GL group had smaller increases in triglycerides [median (interquartile range): 49 (19, 70) compared with 93 (34, 129) mg/dL; P = 0.03] and total cholesterol [13 (0, 36) compared with 33 (22, 56) mg/dL, P = 0.04] and a greater decrease in C-reactive protein [-2.5 (-5.5, -0.7) compared with -0.4 (-1.4, 1.5) mg/dL, P = 0.007]. CONCLUSIONS A low-GL diet resulted in longer pregnancy duration, greater infant head circumference, and improved maternal cardiovascular risk factors. Large-scale studies are warranted to evaluate whether dietary intervention during pregnancy aimed at lowering GL may be useful in the prevention of prematurity and other adverse maternal and infant outcomes. This trial is registered at clinicaltrials.gov as NCT00364403.

Hepatic Steatosis and Increased Adiposity in Mice Consuming Rapidly vs. Slowly Absorbed Carbohydrate

Objective: Non‐alcoholic fatty liver disease (NAFLD) is fast becoming a major public health concern, coincident with the increasing prevalence of obesity. Although lifestyle greatly influences development of NAFLD, the specific dietary causes remain largely unknown. The purpose of this study was to determine whether a diet high in rapidly absorbed carbohydrate (RAC) vs. slowly absorbed carbohydrate (SAC), controlled for confounding dietary factors, causes NAFLD in mice with similar body weight. An animal model was chosen because of logistical and ethical challenges to conducting this study in humans.

Long-term effects of dietary glycemic index on adiposity, energy metabolism, and physical activity in mice

A high-glycemic index (GI) diet has been shown to increase adiposity in rodents; however, the long-term metabolic effects of a low- and high-GI diet have not been examined. In this study, a total of 48 male 129SvPas mice were fed diets high in either rapidly absorbed carbohydrate (RAC; high GI) or slowly absorbed carbohydrate (SAC; low GI) for up to 40 wk. Diets were controlled for macronutrient and micronutrient content, differing only in starch type. Body composition and insulin sensitivity were measured longitudinally by DEXA scan and oral glucose tolerance test, respectively. Food intake, respiratory quotient, physical activity, and energy expenditure were assessed using metabolic cages. Despite having similar mean body weights, mice fed the RAC diet had 40% greater body fat by the end of the study and a mean 2.2-fold greater insulin resistance compared with mice fed the SAC diet. Respiratory quotient was higher in the RAC group, indicating comparatively less fat oxidation. Although no differences in energy expenditure were observed throughout the study, total physical activity was 45% higher for the SAC-fed mice after 38 wk of feeding. We conclude that, in this animal model, 1) the effect of GI on body composition is mediated by changes in substrate oxidation, not energy intake; 2) a high-GI diet causes insulin resistance; and 3) dietary composition can affect physical activity level.